Can anyone enlighten me how to pass a 2D array created in cython to a cdef function? I can do that with 1D array, but not with 2D (or higher), let me illustrate the situation:
This is the C code that I would like to reproduce in cython:
#include <stdio.h>
void print_my_1Darray();
void print_my_2Darray();
int main(void){
int arr1D[] = {1,2,3,4,5,6,7,8,9,10,11,12};
int arr2D[3][4] = {{1,2,3,4},{5,6,7,8},{9,10,11,12}};
print_my_1Darray(arr1D);
printf("\n");
print_my_2Darray(arr2D);
printf("\n");
return 0;
}
void print_my_1Darray( int x[] ){
int i;
for(i=0; i < 12; i++){
printf("c[%d] = %d\n",i, x[i]);
}
}
void print_my_2Darray( int x[3][4] ){
int i, j;
for(i=0; i < 3; i++){
for(j=0; j < 4; j++){
printf("c[%d][%d] = %d\n",j, i, x[i][j]);
}
}
}
And then if I try to reproduce this in Cython like this:
cimport cython
import numpy as np
cimport numpy as cnp
def testfunc():
cdef int *arr1D = [1,2,3,4,5,6,7,8,9,10,11,12]
print_my_1D_array(arr1D)
cdef int *arr2D = [[1,2,3,4], [5,6,7,8], [9,10,11,12]] # <-- WRONG!
print_my_2D_array(arr2D)
cdef void print_my_1D_array(int c_arr[12]):
cdef int i
for i in range(4):
print c_arr[i]
cdef void print_my_2D_array(int c_arr[3][4]):
cdef int i, j
for i in range(3):
for j in range(4):
print c_arr[i][j]
and when I compile this pyx script I get the error:
cdef int *arr2D = [[1,2,3,4][5,6,7,8][9,10,11,12]]
print_my_2D_array(arr2D)
^
------------------------------------------------------------
test2.pyx:18:27: Cannot assign type 'int *' to 'int (*)[4]'
It seems that I can create something with the
"cdef int *arr2D = [[1,2,3,4][5,6,7,8][9,10,11,12]]"
line and it compiles ok until I try to pass it to a function or simply print it's members...
Can anyone explain what's happening there and how to create pure-c 2D/3D arrays in cython and how to pass them to c-level functions? Also, I am trying to avoid numpy arrays there to avoid python overhead, as my code will require very fast calculations on arrays.
You need to make your input array static:
cdef int arr2D[3][4]
arr2D[0][:] = [1, 2, 3, 4]
arr2D[1][:] = [5, 6, 7, 8]
arr2D[2][:] = [9, 10, 11, 12]